US 7,548,433 B2 · Apparatus and method for setting adequate drive strength based upon DC trace resistance

Abstract

An information handing system having apparatus for setting adequate drive strength based upon direct current (DC) trace resistance uses a resistance detection traces for each signal layer of a printed circuit board. These resistance detection traces are coupled to pull-up resistors and routed with a length and cross-sectional geometry that is substantially equal to the worst case routing of a net on a bus that is to be free of receiver mask violations (inadequate received signal strengths). Reference voltage levels may be determined for each bus so as to be representative of the minimum voltage acceptable to guarantee that the worst-case DC trace resistance will not cause the bus waveforms to fail signal integrity. A voltage comparator circuit may be used to compare the determined reference voltage levels with the voltage levels of the resistance detection traces of each of the printed circuit board layers. When the voltage comparator determines that a resistance detection trace voltage is too low, an output from the voltage comparator may be used to generate an error message to a general purpose input-output (GPIO) that may initiate programming (e.g., change the flash memory) of a bus controller so as to use the next higher drive strength setting.

Claims27

Dependent claims

An information handing system having apparatus for setting adequate drive strength based upon direct current (DC) trace resistance, said system comprising:

a printed circuit board, the printed circuit board having at least one layer of conductive signal traces;
a resistance detection trace, wherein the resistance detection trace is configured to have characteristics substantially the same as a worst case signal trace of the at least one layer of conductive signal traces;
a test voltage coupled to a first end of the resistance detection trace;
a trace termination resistor coupled to a second end of the resistance detection trace;
a voltage comparator having a first input coupled to the second end of the resistance detection trace and the trace termination resistor;
a drive strength reference voltage coupled to a second input of the voltage comparator, wherein
if a voltage at the second end of the resistance detection trace is greater than the drive strength reference voltage at the second input then the voltage comparator has an output at a first logic level, and
if a voltage at the second end of the resistance detection trace is less than or equal to the drive strength reference voltage at the second input then the voltage comparator has an output at a second logic level.

5 more elements

An information handing system having apparatus for setting adequate drive strength based upon direct current (DC) trace resistance, said system comprising:

a printed circuit board, the printed circuit board having a plurality of conductive signal trace layers;
a plurality of resistance detection traces, each of the plurality of resistance detection traces has a corresponding layer of the plurality of conductive signal trace layers, wherein each of the plurality of resistance detection traces is configured to have characteristics substantially the same as a worst case signal trace of the corresponding one of the plurality of conductive signal trace layers;
a test voltage coupled to a first end of each of the plurality of resistance detection traces;
a plurality of trace termination resistors having corresponding ones coupled to a second end of each of the plurality of resistance detection traces;
a plurality of voltage comparators, each having a first input coupled to the second end of the corresponding one of the plurality of resistance detection traces and the corresponding one of the plurality of trace termination resistors;
a drive strength reference voltage coupled to a second input of the plurality of voltage comparator, wherein,
if a voltage at the second end of a one of the plurality of resistance detection traces is greater than the drive strength reference voltage at the second input then the corresponding one of the plurality of voltage comparators has an output at a first logic level, and
if a voltage at the second end of the one of the plurality of resistance detection traces is less than or equal to the drive strength reference voltage at the second input then the corresponding one of the plurality of voltage comparators has an output at a second logic level.

5 more elements

Dependencies are inferred from the claim text.

Apparatus and method for setting adequate drive strength based upon DC trace resistance

Life of this patent

Apparatus and method for setting adequate drive strength based upon DC trace resistance

Life of this patent

Abstract

Claims27